In the third episode of Season 8 of "Castle," Rick (Nathan Fillion) goes undercover as a professor, after a college fraternity student dies in the most gruesome way.

TV Guide reports early in their investigation, he and Capt. Beckett (Stana Katic) "unearth some sinister secrets the university wants to keep suppressed."

Castle and Beckett are together again in the episode, entitled "PH Dead," but perhaps not in the way fans have become accustomed to. The still newlywed couple split at the end of Episode 2, when Beckett, perhaps motivated by her desire to keep her husband safe from the assassins who are now tracking her, packed her bags and left.

Meanwhile, aware that he and his wife first grew attracted to one another by solving cases together, Castle digs deeper and deeper into the university mystery, hoping that the case might help him win his wife back.

It recently became clear that all the intrigue and danger that now surrounds Beckett stems from her days in the Attorney General's office. During the second episode, she received a call from former coworker Vikram Singh (Sunkrish Bala), alerting her to a "life or death" situation.

Later, the pair met up, and he informed her that everyone she used to work with is already dead. He added the two of them could be the killer's next targets, seemingly prompting Beckett to put some distance between herself and her new husband.

"Castle" airs Monday nights on ABC. The series also stars Tamala Jones as medical examiner Lanie Parish, Jon Huertas as NYPD Detective Javier Esposito, Seamus Dever as NYPD Detective Kevin Ryan, Molly Quinn as Alexis Castle, and Susan Sullivan as Martha Rodgers.

For the new season, "The Neighbors" alum Toks Olagundoye has joined the series as security specialist Hayley Vargas.